The present invention relates to a shock sensor, and more particularly to a shock sensor which detects whether or not a shock force has been applied to the sensor and displays this fact.
When transporting a precision apparatus such as an electronics equipment unit by a truck and the like, a problem might happen in which the precision apparatus gets damaged by an externally applied shock force. In order to detect whether a shock has been applied, generally, a shock sensor for displaying this fact is attached to the precision apparatus before it is transported.
A conventional shock sensor of such an above type is, for example, the shock sensor having a structure shown in FIG. 1. When an acceleration (shock force) is applied to the shock sensor in a direction indicated by an arrow A, a U-shaped weight 2 provided in a box-like case 1 slides in the direction indicated by the arrow A to presses a leaf spring 3 and deform it in the direction indicated by the arrow A. When the acceleration exceeds a predetermined value, the leaf spring 3 is deformed into a reversely bent state from an original state due to buckling thereof. An indicating plate 4 provided on the leaf spring 3 is moved by the movement of the weight 2 to be maintained in a shock detected position opposite to a displaying window 1a. Since the indicating plate 4 is colored a bright color, such as red, it is easy to recognize whether or not the indicating plate 4 is at the shock detected position from outside by looking for such a bright color through the displaying window 1a. An example of this type of prior art sensor is disclosed in U.S. Pat. No. 3,623,449 issued Nov. 30, 1971 to Knutson.
In the above mentioned shock sensor, since the weight 2 slides inside the case 1, a friction resistance is generated between the weight 2 and the case 1. When the shock sensor is mass-produced, the respective friction resistances for such shock sensor units do not become exactly equal to each other. Accordingly, a dispersion of detected acceleration by means of the movement of weight 2 occurs; resulting in each sensor detecting an acceleration different from the predetermined value. Additionally, due to the relatively heavy weight of the indicating plate 4, the leaf spring 3 and the indicating plate 4 may return to their original positions, that is, their states before the acceleration is detected, when reverse acceleration is applied after the shock sensor has detected a predetermined acceleration. Therefore, there is a problem in that the conventional shock sensor has low reliability.